1. General Background
Pain and overuse disorders of the joints in the body is a common problem. The weight-bearing and articulating surfaces of the knees, and of other joints, are covered with a layer of soft tissue that typically comprises a significant amount of hyaline cartilage. The friction between the cartilage and the surrounding parts of the joint is very low, which facilitates movement of the joints under high pressure. The cartilage is however prone to damage due to disease, injury or chronic wear. Moreover it does not readily heal after damages, as opposed to other connective tissue, and if healed the durable hyaline cartilage is often replaced by less durable fibrocartilage. This means that damages of the cartilage gradually become worse. Along with injury/disease comes a problem with pain which results in handicap and loss of function. It is therefore important to have efficient means and methods for repairing damaged cartilage in knee joints.
The advantages of implants have stimulated a further development of smaller implants that can be implanted with less invasive surgery. In this development there has also been an effort to achieve small joint implants, suitable for repair of a small cartilage injury that have a minimal influence on the surrounding parts of the joint. In the surgical operation of implanting such small implants it is critical that the implant is positioned in a precise manner. If the implant is offset from its intended position it may cause an increased wear or load on the joint. For example, if the implant is tilted this may result in an edge that projects above the cartilage surface and causes wear on the opposing cartilage in the joint. Another example is the case that the implant is placed in a too shallow position, which may result in a too high top of the implant that causes the joint to articulate in an uneven manner and increase the load on an opposing point of the joint. For the patient, also small misplacements or deviations from an ideal position may result in pain, longer time for convalescence or even a surgical operation being done in vain and making it more difficult to repair the damage in the joint. A large burden is therefore placed on the surgeon not to misplace or misfit the implant. There is therefore a need for well fitting implants as well as tools that are designed to relieve and support the surgeon in the implant surgery.
The design of the implant and the surgical tools, in other words, the design of the surgical kit is crucial for the outcome of the implants life-time in a joint. Also, the parameters for designing are of uttermost importance for the result in these operations. Small differences in the design can make a huge difference in fit and life-time of an implant in the body, convalescence time for the patient, economic values due o surgery time, success of operations, also the number of successful operations will increase and the working conditions for the surgeon will be improved if the designing parameters are selected right.
2. Specific Background
Another important factor for achieving high quality implants and efficient implantation is the manufacturing system. Various methods of manufacturing patient specific implants are known.